foo.c: In function 'main':
foo.c:4:9: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
    4 |         printf("输入正整数");
      |         ^~~~~~
foo.c:1:1: note: include '<stdio.h>' or provide a declaration of 'printf'
  +++ |+#include <stdio.h>
    1 | int main()
foo.c:4:9: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
    4 |         printf("输入正整数");
      |         ^~~~~~
foo.c:4:9: note: include '<stdio.h>' or provide a declaration of 'printf'
foo.c:5:9: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    5 |         scanf("%d",&n);
      |         ^~~~~
foo.c:5:9: note: include '<stdio.h>' or provide a declaration of 'scanf'
foo.c:5:9: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
foo.c:5:9: note: include '<stdio.h>' or provide a declaration of 'scanf'

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